The objective of this project is to study the enzyme purine nucleoside phosphorylase from lymphoid cells and other human blood cells in an attempt to establish the relationship between enzymatic deficiency and immunodeficiency. The presence and the levels of the enzyme in separated T and B lymphocytes and monocytes from human peripheral blood will be determined as well as enzyme changes that may accompany stimulation of the above cells by mitogens and antigens. The enzyme will be purified from separated T and B lymphocytes, monocytes, blasts and macrophages and will be analyzed by two dimensional gel electrophoresis to determine the state of subunit modification. The effect of subunit composition on the kinetic and catalytic properties of the enzyme will be assessed by electrophoretic techniques.